DLP projectors use one or more digital micromirror devices (DMD) to reflect light and produce a picture. Each DMD may contain more than 2 million pixel mirrors, and using pulse-width modulation (PWM), each pixel mirror is capable of producing various levels of light intensity, or shades between white and black. In PWM, each pixel mirror is rapidly repositioned (generally termed ‘on’ for white, and ‘off’ for black) in response to data bits. As such, each pixel within a picture appears to have an intermediate intensity proportional to the fraction of time the corresponding pixel mirror is on.
While each individual pixel mirror is subjected to a unique pulse sequence to achieve a desired pixel shade, similar pixel shades can have similar pulse sequences. Where a grouping of pixel mirrors in a given area of the DMD are called to exhibit similar shades, the end effect within that region can be a “block” of pixels in either an on state or an off state. This effect, herein referred to as “patterning” results in large-scale patterns at any instantaneous moment.
For single projector applications, patterning does not pose much of an issue to the viewer. Problems arise, however, in multiple-projector applications such as multiple-projector displays where electronic edge blending in the blend zone is used. It has been noted that in the blend zone, the overlapping of the aforementioned patterning results in visual artefacts most noticeable for solid colors (such as a blue sky) during eye saccades. While these visual artefacts may take on a variety of forms, they can generally be described as irregular banding patterns of increased and decreased light intensity relative to the regions adjacent the blend zone.